Normal Organ Radiation Dosimetry and Associated Uncertainties in Nuclear Medicine, with Emphasis on Iodine-131

The prophylactic antiemetic therapies in management of differentiated thyroid cancer patients with radioactive iodine therapy: a single-center, non-randomized clinical trial

Objective

The present study was to investigate three different single-drug regimens to show which was more effective to reduce radioactive iodine therapy (RAI) associated nausea and vomiting, and to compare the occurrence of long-term gastrointestinal diseases after RAI therapy.

Method

We performed a single-center, non-randomized clinical trial among patients who underwent RAI therapy from March 2016 to July 2022. Enrolled patients were divided into four cohorts based on the date of the treatment. cohort 1, with no preventive antiemetics; cohort 2, received 20 mg of pantoprazole per day for 3 days; cohort 3, received a 10 mg metoclopramide tablet two times daily for 3 days; cohort 4, oral ondansetron, 8 mg, twice daily for 3 days. The primary endpoints were proportion of patients who experience vomiting episodes and nausea during the 7-day hospital period. Secondary end points included Functional Living Index Emesis (FLIE) quality-of life questionnaires and the occurrence of gastrointestinal diseases.

Results

A total of 1755 patients were analyzed, comprised of 1299 (74.0%) women and 456 (26.0%) men, with a median age of 44 years (range 18-78 years). The characteristics of patient were similar within the four groups. 465 (26.4%) patients developed RAI-associated nausea, and 186 (14.4%) patients developed RAI-associated vomiting. The rate of nausea was significantly decreased in the patients who were taking ondansetron when compared with the other cohorts (P<0.05), while the rate of vomiting (≥6 episodes) was slightly lower. As secondary endpoint, FLIE measures ondansetron scored highly compared to other cohorts, from baseline (mean score of 110.53 ± 17.54) to day 7 (mean score of 105.56 ± 12.48). In addition, 48 (2.7%) patients were found to be with gastrointestinal diseases at the end of one year follow up. Multiple RAI therapy and higher dose of I-131 per body weight revealed a significantly independent risk factors of developing gastrointestinal disorders.

Conclusions

In conclusion, the present study demonstrated that short-term ondansetron could be an effective prophylactic agent in controlling RAI-associated nausea and vomiting. Furthermore, the risk of developing gastrointestinal disorders was significantly higher for patients with multiple RAI therapy and higher dose of I-131 per body weight.

Retrospective Evaluation of Cytogenetic Effects Induced by Internal Radioiodine Exposure: A 27-Year Follow-Up Study

Radioiodine (131I) is widely used in the treatment of hyperthyroidism and as an effective ablative therapy for differentiated thyroid cancer. Radioiodine (131I) constitutes 90% of the currently used therapies in the field of nuclear medicine. Here, we report the cytogenetic findings of a long-term follow-up study of 27 years on a male patient who received two rounds of radioiodine treatment within a span of 26 months between 1992 and 1994 for his papillary thyroid cancer. A comprehensive cytogenetic follow-up study utilizing cytokinesis blocked micronucleus assay, dicentric chromosome assay, genome wide translocations and inversions was initiated on this patient since the first administration of radioiodine in 1992. Frequencies of micronuclei (0.006/cell) and dicentric chromosomes (0.008/cell) detected in the current study were grossly similar to that reported earlier in 2019. The mFISH analysis detected chromosome aberrations in 8.6% of the cells in the form of both unbalanced and balanced translocations. Additionally, a clonal translocation involving chromosomes 14p; 15q was observed in 2 of the 500 cells analyzed. Out of the 500 cells examined, one cell showed a complex translocation (involving chromosomes 9, 10, and 16) besides 5 other chromosome rearrangements. Collectively, our study indicates that the past radioiodine exposure results in long-lasting chromosome damage and that the persistence of translocations can be useful for both retrospective biodosimetry and for monitoring chromosome instability in the lymphocytes of radioiodine exposed individuals.

Radioactive Iodine Treatment for Thyroid Cancer Patients Increases the Risk of Long-Term Gastrointestinal Disorders: A Nationwide Population-Based Cohort Analysis

Simple Summary

The standard treatment for well-differentiated thyroid cancer is thyroidectomy followed by radioactive iodine (RAI) treatment or active surveillance. Despite adequate documentation of acute gastrointestinal adverse effects after RAI treatment, whether the gastrointestinal exposure causes long-term comorbidity or not remained unclear. We conducted a nationwide, population-based retrospective cohort study using the data from the Taiwan National Health Insurance Research Database (NHIRD) to clarify the association between long-term gastrointestinal disorders (including ulcers, atrophic gastritis, and secondary stomach malignancy) and RAI treatment in thyroid cancer patients. We found that patients with RAI treatment were at a significantly higher risk of developing gastric and duodenal ulcers than those without. In addition, a higher cumulative dose is associated with higher risk. Therefore, follow-ups at gastrointestinal clinics might be of great importance for patients presenting with chronic gastrointestinal discomforts, after receiving a single RAI dose of more than 1.11 GBq, and undergoing repeated treatment due to recurrent or residual thyroid cancer.

Abstract

(1) Background: The study aimed to investigate the association between radioactive iodine (RAI) treatment and long-term gastrointestinal disorders including ulcers, atrophic gastritis, and secondary malignant neoplasm of the stomach in patients with thyroid cancer. (2) Methods: The data of the study were extracted from the National Health Insurance Database (NHIRD) of Taiwan between 2000 to 2015. Patients of ages older than 20 with thyroid cancer after thyroidectomy were included and divided into groups with RAI (study cohort) and without RAI (comparison cohort). Multivariate Cox proportional hazards regression analysis and the Kaplan–Meier method were used for statistical analysis. (3) Results: A total of 7250 (with RAI: 5800, without RAI: 1450) patients were included. The Kaplan-Meier analysis revealed a significantly higher cumulative risk for overall gastrointestinal disorders in the group with RAI (log-rank p = 0.034). The risk for gastrointestinal disorders was higher when receiving a cumulative RAI dose higher than 1.11 GBq in the Cox regression analysis. In the subgroup analysis, the risks of gastric and duodenal ulcers are significantly higher in the group with RAI treatment. (4) Conclusions: This study revealed that RAI was associated with an increased risk for long-term gastrointestinal disorders, specifically gastric and duodenal ulcers, in thyroid cancer, especially when the cumulative dose exceeds 1.11 GBq.

Evaluation of the physical and biological dosimetry methods in iodine-131-treated patients

The aim of the study was to compare physical and biological dosimetry methods in iodine-131 (I-131)-receiving patients. The present study comprised of 47 patients (mean age: 47.9 ± 15.8 years), treated with I-131. Group I consisted of 17 patients with hyperthyroidism and mean administered activity of this group was 432.9 ± 111 MBq. There were 15 follow-up patients of differentiated thyroid cancer (DTC) in Group II with mean administered activity of 185 ± 22.2 MBq, who were administered scanning dose of I-131. Group III comprised of 15 patients with DTC, ablated with high-dose of I-131, and this group's mean administered activity was 4347.5 ± 695.6 MBq. The whole-body absorbed doses were calculated in all patients both with the Medical Internal Radiation Dosimetry (MIRD) method using MIRDOSE3 software and cytokinesis-block micronucleus (MN) assay-based MN analysis and were compared. The whole-body absorbed dose, calculated by MIRD method, showed very good correlation with the administered I-131 activity (r = 0.89, P < 0.001), but it was moderate in the MN method (r = 0.52, P < 0.01). Absorbed dose estimations with MIRD method were 49.2 ± 20.8 mGy in Group I, 6.5 ± 1.6 mGy in Group II, and 154.3 ± 47.8 mGy in Group III; the differences were statistically significant (P < 0.001), as expected. Pre- and posttreatment MN frequencies differed significantly in all groups (P < 0.05). The whole-body absorbed doses, based on MN method, were 68.2 ± 17.5, 46.0 ± 11.4, and 90.5 ± 26.9 mGy in Groups I–III, respectively. The difference was significant between Group II and Group III (P < 0.01). The mean absorbed dose was 74.6 ± 27.9 mGy with MN versus 68.0 ± 67.1 mGy in MIRD method (P = 0.087) in the entire study population and the correlation was moderate (r = 0.73, P < 0.001). The whole-body absorbed doses, estimated by MN method, showed moderate correlation with administered radioiodine activities in low radioiodine doses and had significantly different and fluctuating values as compared to MIRD method in patients treated with I-131.

Cytogenetic biodosimetry and dose-rate effect after radioiodine therapy for thyroid cancer

This study set out to investigate chromosomal damage in peripheral blood lymphocytes of thyroid cancer patients receiving ¹³¹I for thyroid remnant ablation or treatment of metastatic disease. The observed chromosomal damage was further converted to the estimates of whole-body dose to project the adverse side effects. Chromosomal aberration analysis was performed in 24 patients treated for the first time or after multiple courses. Blood samples were collected before treatment and 3 or 4 days after administration of 2-4 GBq of ¹³¹I. Both conventional cytogenetic and chromosome 2, 4 and 12 painting assays were used. To account for dose-rate effect, a dose-protraction factor was applied to calculate the whole-body dose. The mean dose was 0.62 Gy (95% CI: 0.44-0.77 Gy) in the subgroup of patients treated one time and 0.67 Gy (95% CI: 0.03-1.00 Gy) in re-treated patients. These dose estimates are about 1.7-fold higher than those disregarding the effect of exposure duration. In re-treated patients, the neglected dose-rate effect can result in underestimation of the cumulative whole-body dose by the factor ranging from 2.6 to 6.8. Elevated frequency of chromosomal aberrations observed in re-treated patients before radioiodine therapy allows estimation of a cumulative dose received from all previous treatments.

Gaussian plume atmospheric modelling and radiation exposure calculations following the cremation of a deceased thyroid cancer patient treated with iodine-131

Shortly after treatment with 7200 MBq of ¹³¹I, a thyroid cancer patient died and was subsequently cremated. Calculations of the atmospheric emissions of ¹³¹I from the crematorium flue were performed using a standard atmospheric pollution Gaussian Plume Dispersal model. Estimates of whole-body and thyroid dose of those potentially exposed were made using OLINDA/EXM dosimetry software. Under the meteorological conditions prevalent at the time of the cremation, and depending on the actual release rate of the ¹³¹I, the Western Australian legal limit of 3.7 Bqm^-3 for atmospheric emissions of ¹³¹I may have been exceeded for distances of up to 440 and 1610 m downwind of the crematorium chimney, with the maximum concentration being between 33 and 392 Bqm^-3. Assuming 16% of the inhaled ¹³¹I was taken up in the thyroid with the balance in the remainder of the body, the radiation dose to maximally exposed individuals was calculated to be approximately 17.7 μSv to the thyroid and 0.04 μSv to the whole-body. Despite the maximum allowable atmospheric ¹³¹I concentration of 3.7 Bqm^-3 being exceeded, as the number of people immediately downwind of the crematorium flue in the high concentration zones was very low, and considering the relatively high tolerable dose to the thyroid, the radiation dose to people was probably not a problem in this case. The local limit of 1000 MBq of ¹³¹I for the cremation of a deceased patient is reasonable, but with adequate precautions could be significantly increased without any harmful effects to people or the environment.

Cytogenetic effects of radioiodine therapy: a 20-year follow-up study

The purpose of this study was to compare cytogenetic data in a patient before and after treatment with radioiodine to evaluate the assays in the context of biological dosimetry. We studied a 34-year-old male patient who underwent a total thyroidectomy followed by ablation therapy with (131)I (19.28 GBq) for a papillary thyroid carcinoma. The patient provided blood samples before treatment and then serial samples at monthly intervals during the first year period and quarterly intervals for 5 years and finally 20 years after treatment. A micronucleus assay, dicentric assay, FISH method and G-banding were used to detect and measure DNA damage in circulating peripheral blood lymphocytes of the patient. The results showed that radiation-induced cytogenetic effects persisted for many years after treatment as shown by elevated micronuclei and chromosome aberrations as a result of exposure to (131)I. At 5 years after treatment, the micronucleus count was tenfold higher than the pre-exposure frequency. Shortly after the treatment, micronucleus counts produced a dose estimate of 0.47 ± 0.09 Gy. The dose to the patient evaluated retrospectively using FISH-measured translocations was 0.70 ± 0.16 Gy. Overall, our results show that the micronucleus assay is a retrospective biomarker of low-dose radiation exposure. However, this method is not able to determine local dose to the target tissue which in this case was any residual thyroid cells plus metastases of thyroidal origin.

Organ Dose Estimates for Hyperthyroid Patients Treated with (131)I: An Update of the Thyrotoxicosis Follow-Up Study

The Thyrotoxicosis Therapy Follow-up Study (TTFUS) is comprised of 35,593 hyperthyroid patients treated from the mid-1940s through the mid-1960s. One objective of the TTFUS was to evaluate the long-term effects of high-dose iodine-131 ((131)I) treatment (1-4). In the TTFUS cohort, 23,020 patients were treated with (131)I, including 21,536 patients with Graves disease (GD), 1,203 patients with toxic nodular goiter (TNG) and 281 patients with unknown disease. The study population constituted the largest group of hyperthyroid patients ever examined in a single health risk study. The average number (± 1 standard deviation) of (131)I treatments per patient was 1.7 ± 1.4 for the GD patients and 2.1 ± 2.1 for the TNG patients. The average total (131)I administered activity was 380 ± 360 MBq for GD patients and 640 ± 550 MBq for TNG patients. In this work, a biokinetic model for iodine was developed to derive organ residence times and to reconstruct the radiation-absorbed doses to the thyroid gland and to other organs resulting from administration of (131)I to hyperthyroid patients. Based on (131)I data for a small, kinetically well-characterized sub-cohort of patients, multivariate regression equations were developed to relate the numbers of disintegrations of (131)I in more than 50 organs and tissues to anatomical (thyroid mass) and clinical (percentage thyroid uptake and pulse rate) parameters. These equations were then applied to estimate the numbers of (131)I disintegrations in the organs and tissues of all other hyperthyroid patients in the TTFUS who were treated with (131)I. The reference voxel phantoms adopted by the International Commission on Radiological Protection (ICRP) were then used to calculate the absorbed doses in more than 20 organs and tissues of the body. As expected, the absorbed doses were found to be highest in the thyroid (arithmetic means of 120 and 140 Gy for GD and TNG patients, respectively). Absorbed doses in organs other than the thyroid were much smaller, with arithmetic means of 1.6 Gy, 1.5 Gy and 0.65 Gy for esophagus, thymus and salivary glands, respectively. The arithmetic mean doses to all other organs and tissues were more than 100 times less than those to the thyroid gland. To our knowledge, this work represents the most comprehensive study to date of the doses received by persons treated with (131)I for hyperthyroidism.

Radioiodine therapy in benign thyroid diseases: effects, side effects, and factors affecting therapeutic outcome

Radioiodine ((131)I) therapy of benign thyroid diseases was introduced 70 yr ago, and the patients treated since then are probably numbered in the millions. Fifty to 90% of hyperthyroid patients are cured within 1 yr after (131)I therapy. With longer follow-up, permanent hypothyroidism seems inevitable in Graves' disease, whereas this risk is much lower when treating toxic nodular goiter. The side effect causing most concern is the potential induction of ophthalmopathy in predisposed individuals. The response to (131)I therapy is to some extent related to the radiation dose. However, calculation of an exact thyroid dose is error-prone due to imprecise measurement of the (131)I biokinetics, and the importance of internal dosimetric factors, such as the thyroid follicle size, is probably underestimated. Besides these obstacles, several potential confounders interfere with the efficacy of (131)I therapy, and they may even interact mutually and counteract each other. Numerous studies have evaluated the effect of (131)I therapy, but results have been conflicting due to differences in design, sample size, patient selection, and dose calculation. It seems clear that no single factor reliably predicts the outcome from (131)I therapy. The individual radiosensitivity, still poorly defined and impossible to quantify, may be a major determinant of the outcome from (131)I therapy. Above all, the impact of (131)I therapy relies on the iodine-concentrating ability of the thyroid gland. The thyroid (131)I uptake (or retention) can be stimulated in several ways, including dietary iodine restriction and use of lithium. In particular, recombinant human thyrotropin has gained interest because this compound significantly amplifies the effect of (131)I therapy in patients with nontoxic nodular goiter.

Comparison of internal dosimetry factors for three classes of adult computational phantoms with emphasis on I-131 in the thyroid

The S values for 11 major target organs for I-131 in the thyroid were compared for three classes of adult computational human phantoms: stylized, voxel and hybrid phantoms. In addition, we compared specific absorbed fractions (SAFs) with the thyroid as a source region over a broader photon energy range than the x- and gamma-rays of I-131. The S and SAF values were calculated for the International Commission on Radiological Protection (ICRP) reference voxel phantoms and the University of Florida (UF) hybrid phantoms by using the Monte Carlo transport method, while the S and SAF values for the Oak Ridge National Laboratory (ORNL) stylized phantoms were obtained from earlier publications. Phantoms in our calculations were for adults of both genders. The 11 target organs and tissues that were selected for the comparison of S values are brain, breast, stomach wall, small intestine wall, colon wall, heart wall, pancreas, salivary glands, thyroid, lungs and active marrow for I-131 and thyroid as a source region. The comparisons showed, in general, an underestimation of S values reported for the stylized phantoms compared to the values based on the ICRP voxel and UF hybrid phantoms and relatively good agreement between the S values obtained for the ICRP and UF phantoms. Substantial differences were observed for some organs between the three types of phantoms. For example, the small intestine wall of ICRP male phantom and heart wall of ICRP female phantom showed up to eightfold and fourfold greater S values, respectively, compared to the reported values for the ORNL phantoms. UF male and female phantoms also showed significant differences compared to the ORNL phantom, 4.0-fold greater for the small intestine wall and 3.3-fold greater for the heart wall. In our method, we directly calculated the S values without using the SAFs as commonly done. Hence, we sought to confirm the differences observed in our S values by comparing the SAFs among the phantoms with the thyroid as a source region for selected target organs--small intestine wall, lungs, pancreas and breast--as well as illustrate differences in energy deposition across the energy range (12 photon energies from 0.01 to 4 MeV). Differences were found in the SAFs between phantoms in a similar manner as the differences observed in S values but with larger differences at lower photon energies. To investigate the differences observed in the S and SAF values, the chord length distributions (CLDs) were computed for the selected source--target pairs and compared across the phantoms. As demonstrated by the CLDs, we found that the differences between phantoms in those factors used in internal dosimetry were governed to a significant degree by inter-organ distances which are a function of organ shape as well as organ location.

Effective dose: practice, purpose and pitfalls for nuclear medicine

Effective dose (E) is the only comparatively simple dose quantity that is related to health detriment for stochastic effects from exposure to ionising radiation. As such, E has found wide application for medical exposures, as it allows comparisons with doses from different examinations and other sources. E is derived from the weighted sum of doses to tissues known to be sensitive to radiation from epidemiological studies and contains inherent approximations. Thus it is not a scientific quantity, but a practical one that the International Commission on Radiological Protection (ICRP) has created for use in the calculation of reference doses for protection purposes. In the application of E to medical exposures, there has been a tendency to attribute a greater accuracy to values of E than is justified by its derivation. Recognising that E is strictly not subject to uncertainties, an analysis has been undertaken of potential uncertainties in E for different nuclear medicine examinations to enable users to judge its reliability as a comparator of relative risk. Assessments have been based on the considered accuracy of the component parts and indicate that the uncertainties in the values of E as a relative indicator of harm for nuclear medicine procedures for a reference patient are about ± 50%. These are larger than those for radiology procedures, because of the tendency for doses to single organs, especially the bladder, to form a substantial part of E for some procedures. Revision of the tissue weighting factors in 2007 produced a 10% decrease in the mean value of E for nuclear medicine examinations. Estimations of cancer risk based on E for an individual could vary by one or two orders of magnitude. E fulfils an important role as a health-related dose quantity that can be used in justification of nuclear medicine examinations, but physicians should be aware of its limitations. General terminology should be used in conveying risks to patients and medical professionals.

Effective dose: how should it be applied to medical exposures?

The effective dose (E) was created to provide a dose quantity that was related to the probability of health detriment due to stochastic effects from exposure to low doses of ionizing radiation. E is derived from the weighted sum of doses to tissues that are known to be sensitive to radiation and so can only be derived by calculation. The tissue weighting factors are derived from the extrapolation of epidemiological evidence. E was intended for use in radiation protection, but has found wide application in evaluation of doses for medical exposures involving only parts of the body. More reliance is often placed on E values and risk estimates based on E than the evidence on which it is based can justify. In this paper, the uncertainties in the estimated values of E for a reference patient and the associated risk coefficients are reviewed in order to provide an indication of how much reliance can be placed on E as an indicator of risk for patients. The relative uncertainty in estimated values of E for medical exposures for a reference patient is seen to be about +/-40%. The estimated risk of cancer may be a factor of three higher or lower when applied to a reference patient, and will be more variable when applied to an individual. A set of recommendations relating to the use of E and description of risk for medical exposures is proposed.